The present invention relates to a method for separating a saturated fatty acid and an unsaturated fatty acid from a mixture of fatty acids by a dry fractionation process with a superior efficiency, and use of the separated unsaturated fatty acids.
Fatty acids are widely utilized as an intermediate raw material of foods, such as a monoglyceride and a diglyceride, as well as an additive, and an intermediate raw material for other sorts of industrial products. These fatty acids are generally produced by hydrolyzing a vegetable oil such as a rapeseed oil, a soybean oil, or an animal oil such as beef tallow, using a high pressure method, or a decomposition method with an enzyme.
However, fatty acids produced simply by hydrolyzing an animal oil or a vegetable oil as described above, which have natural fatty acid compositions, are not necessarily suitable as a basic raw material for industrial use. In other wards, it is necessary to fractionate unsaturated fatty acids and saturated fatty acids depending on the utilization purpose.
Therefore, it becomes necessary to modify a melting point to obtain a desired mixture of fatty acids. Generally in a fractionation process of fatty acids, a fractionation process using a solvent and a fractionation process using a wetting agent are employed. Although these processes show high efficiencies (e.g. yields) of separation, they pose problems such as an initial cost for facility investment as well as a high running cost for recovery of the solvent or the aqueous solution of the wetting agent and the like. In contrast, a dry fractionation process without using any solvent (e.g. a no solvent process) is an inexpensive fractionation process, and an attempt to solve such problem as low filtration rate, has been made by employing an emulsifier such as a polyglycerol ester of a fatty acid (JP-A-11-106782).
However, even with the dry fractionation process using a polyglycerol ester of a fatty acid, it has become apparent that sufficiently large crystals are not formed under some conditions of cooling rate, retention time or the like, resulting in a low efficiency of filtration.
The present invention provides a method for producing a saturated fatty acid and an unsaturated fatty acid by fractionating the saturated fatty acid and the unsaturated fatty acid by adding and mixing a polyglycerol ester of a fatty acid to a raw fatty acids mixture and cooling them to deposit crystals, wherein a cooling procedure is performed at a cooling rate of 4xc2x0 C./h or less when an supersaturation ratio is 60% or more, and said cooling rate is varied during the cooling.
In addition, the present invention provides a method for producing a glycerides mixture from the unsaturated fatty acids fractionated by the above method, in which at least 90% by mass of the fatty acid components are unsaturated fatty acids.